There are many instances where the detection of parameters such as temperature, pressure, flow rate, voltage, etc., are required in remote or hostile environments. There are a number of materials whose light absorptive properties at certain frequencies, are sensitive to these parameters and application has been made of this property to provide a sensor of these parameters. In such circumstances, light is applied to the sensitive material, for example along an optical fiber, partially transmitted through the material, and returned through a receiver operative to sense a variation in the intensity of the light selectively transmitted through the sensitive material and to provide an output indication of the variations, correlated to the dimension of the parameter being sensed. An example of such an application is shown in U.S. Pat. No. 4,136,566.
The sensitivity of semiconductor materials to such parameters as pressure and temperature is sufficient to permit detection of pressure variations on the order of a thousandth of a pound per square inch. Applications for such sensors in areas of process control, deep ocean investigations, and among others are envisioned.
High optical sensitivities to temperature can also be achieved with semiconductor materials. Indeed, most semiconductor materials will be responsive to both temperature and pressure and in remote applications where both parameters may vary, as well as other parameters which may effect the absorption characteristic of semiconductor materials, the multiple dependency of the semiconductor material to these parameters can reduce the accuracy of the ultimately measured parameter. In addition, environmental effects on long lengths of optical fibers coupling light to and from selectively absorptive semiconductor material can also effect sensing accuracy.